1//===-- PatchableFunction.cpp - Patchable prologues for LLVM -------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file implements edits function bodies in place to support the
10// "patchable-function" attribute.
11//
12//===----------------------------------------------------------------------===//
13
14#include "llvm/CodeGen/MachineFunction.h"
15#include "llvm/CodeGen/MachineFunctionPass.h"
16#include "llvm/CodeGen/MachineInstrBuilder.h"
17#include "llvm/CodeGen/Passes.h"
18#include "llvm/CodeGen/TargetFrameLowering.h"
19#include "llvm/CodeGen/TargetInstrInfo.h"
20#include "llvm/CodeGen/TargetSubtargetInfo.h"
21#include "llvm/InitializePasses.h"
22
23using namespace llvm;
24
25namespace {
26struct PatchableFunction : public MachineFunctionPass {
27  static char ID; // Pass identification, replacement for typeid
28  PatchableFunction() : MachineFunctionPass(ID) {
29    initializePatchableFunctionPass(*PassRegistry::getPassRegistry());
30  }
31
32  bool runOnMachineFunction(MachineFunction &F) override;
33   MachineFunctionProperties getRequiredProperties() const override {
34    return MachineFunctionProperties().set(
35        MachineFunctionProperties::Property::NoVRegs);
36  }
37};
38}
39
40/// Returns true if instruction \p MI will not result in actual machine code
41/// instructions.
42static bool doesNotGeneratecode(const MachineInstr &MI) {
43  // TODO: Introduce an MCInstrDesc flag for this
44  switch (MI.getOpcode()) {
45  default: return false;
46  case TargetOpcode::IMPLICIT_DEF:
47  case TargetOpcode::KILL:
48  case TargetOpcode::CFI_INSTRUCTION:
49  case TargetOpcode::EH_LABEL:
50  case TargetOpcode::GC_LABEL:
51  case TargetOpcode::DBG_VALUE:
52  case TargetOpcode::DBG_LABEL:
53    return true;
54  }
55}
56
57bool PatchableFunction::runOnMachineFunction(MachineFunction &MF) {
58  if (MF.getFunction().hasFnAttribute("patchable-function-entry")) {
59    MachineBasicBlock &FirstMBB = *MF.begin();
60    const TargetInstrInfo *TII = MF.getSubtarget().getInstrInfo();
61    // The initial .loc covers PATCHABLE_FUNCTION_ENTER.
62    BuildMI(FirstMBB, FirstMBB.begin(), DebugLoc(),
63            TII->get(TargetOpcode::PATCHABLE_FUNCTION_ENTER));
64    return true;
65  }
66
67  if (!MF.getFunction().hasFnAttribute("patchable-function"))
68    return false;
69
70#ifndef NDEBUG
71  Attribute PatchAttr = MF.getFunction().getFnAttribute("patchable-function");
72  StringRef PatchType = PatchAttr.getValueAsString();
73  assert(PatchType == "prologue-short-redirect" && "Only possibility today!");
74#endif
75
76  auto &FirstMBB = *MF.begin();
77  MachineBasicBlock::iterator FirstActualI = FirstMBB.begin();
78  for (; doesNotGeneratecode(*FirstActualI); ++FirstActualI)
79    assert(FirstActualI != FirstMBB.end());
80
81  auto *TII = MF.getSubtarget().getInstrInfo();
82  auto MIB = BuildMI(FirstMBB, FirstActualI, FirstActualI->getDebugLoc(),
83                     TII->get(TargetOpcode::PATCHABLE_OP))
84                 .addImm(2)
85                 .addImm(FirstActualI->getOpcode());
86
87  for (auto &MO : FirstActualI->operands())
88    MIB.add(MO);
89
90  FirstActualI->eraseFromParent();
91  MF.ensureAlignment(Align(16));
92  return true;
93}
94
95char PatchableFunction::ID = 0;
96char &llvm::PatchableFunctionID = PatchableFunction::ID;
97INITIALIZE_PASS(PatchableFunction, "patchable-function",
98                "Implement the 'patchable-function' attribute", false, false)
99